Three years ago, our survey of international public health advice showed that agencies around the world advised multi-layered protection¹. Today most of them have narrowed their recommendations to some degree and the World Health Organization stands increasingly alone in still advising multi-layered protections.

In August 2023, we surveyed governments and territories on their official advice for preventing Long Covid¹. Agencies that had previously relied on a vaccines-only strategy had updated their guidance to recommend preventing infection as the best way to avoid Long Covid. Masks and respirators in indoor spaces, clean air policies, ventilation, hand and respiratory hygiene all became part of national guidance, alongside vaccination.

The following July, the US Center for Disease Control went further, publishing an explicit statement that Covid-19 is a year-round threat rather than a winter virus, alongside a graphic setting out multi-layered protection: immunization, hand hygiene, clean air, isolation, treatment, face masks, social distancing and testing².

Three years later, the picture has changed.

What the agencies say now

The following table records what each agency currently recommends to the general public. Because guidance has narrowed, a simple tick or cross would misrepresent several jurisdictions, so we have used three marks:

The World Health Organization still advises multi-layered protection; getting vaccinated, keeping at least a metre from others, avoiding crowds and close contact, wearing a properly fitted mask where distancing is not possible or ventilation is poor, cleaning hands frequently, practicing respiratory hygiene, and avoiding the ‘3Cs’; spaces that are closed, crowded, or involve close contact³.

The United States retains the unified Respiratory Virus Guidance introduced in March 2024, which groups Covid-19 with influenza and RSV under a single symptom-based framework. It advises people to stay away from others until at least 24 hours after symptoms are improving and fever has resolved without medication, then take added precautions; hygiene, masks, physical distancing and steps for cleaner air for a further five days⁴. On Long Covid specifically, the CDC recommends following its core strategies as the best way to lower the risk of severe illness and to prevent Long Covid, and suggests prompt testing and treatment for those with risk factors⁶. The biggest change is on vaccination. The 2025 - 2026 vaccine is recommended for people aged six months and older on the basis of individual decision-making, shared clinical decision-making, rather than as a universal recommendation, with individuals able to self-attest to risk factors⁵. The CDC continues to stress that vaccination matters most for those aged 65 and over, those at high risk of severe illness, and those never previously vaccinated. Avoiding crowded settings, which appeared in the CDC’s 2024 multi-layered graphic, no longer features.

In the United Kingdom, GOV.UK’s Living safely with respiratory infections guidance still covers ventilation, hand and respiratory hygiene, and when to consider a face covering, and it still notes that the risk of catching or passing on Covid-19 is greatest in close proximity or in enclosed and poorly ventilated spaces⁷, but vaccination is described as the best defence, and the guidance explicitly notes that vaccines reduce the risk of long-term symptoms. Distancing as a general measure has gone.

However, eligibility for vaccination has narrowed. The spring 2026 programme covered those aged 75 and over, residents of care homes for older adults, and the immunosuppressed, with UKHSA surveillance showing those vaccinated in the previous spring programme were around 55% less likely to be admitted to hospital with Covid-19 in the following five to nine weeks⁸. A House of Commons Library briefing published in May 2026 records UK evidence that vaccinated individuals were less likely to experience long covid symptoms than unvaccinated people, notes that people with long covid are not automatically eligible for an NHS vaccine, and reports that in February 2026 the government said the Joint Committee on Vaccination and Immunisation considered the evidence in this area to be uncertain⁹. In healthcare settings, revised UKHSA infection prevention and control guidance retains universal face masks for staff and face masks or coverings for patients and visitors in health and care settings¹⁰.

Australia has retained some of the 2023 advice. At a federal level, vaccination is described as the best protection and free to everyone recommended to receive it¹¹. The advice is that people at higher risk of severe illness, long Covid or death should take extra precautions and discuss antiviral eligibility with a doctor¹². At state level the messaging is more explicit: New South Wales Health says the best way to avoid long Covid is to protect yourself from Covid-19 by practising Covid-safe behaviours¹³, which includes staying home when sick, wearing a mask if you must leave home while unwell, not visiting people at higher risk while sick, avoiding crowded places, and meeting outdoors or in large, well-ventilated spaces with open doors and windows¹⁴. The Australian Centre for Disease Control maintains dedicated hand hygiene guidance, advising regular handwashing with soap and water for at least 20 seconds to reduce the spread of germs including those that cause common respiratory disease¹⁵.

Canada maintains a multi-layered position. The Public Health Agency advises staying up to date with vaccination and, in addition, using personal protective measures, noting explicitly that these are most effective when combined: staying home and limiting contact when sick, wearing a well-constructed and well-fitting mask when appropriate, improving indoor ventilation where possible, practising hand hygiene, covering coughs and sneezes, and cleaning high-touch surfaces^16,17. Its indoor ventilation guidance adds that improving air quality must be combined with other public health measures, and that good respiratory and hand hygiene should continue¹⁸. Avoiding crowded settings survives in a weaker form: the Agency identifies small, crowded, poorly ventilated settings as higher risk and advises those at higher risk to use protective measures in such settings rather than avoid them, while recommending gathering outdoors when possible and masking in crowded or closed spaces when travelling^16,17.

Health New Zealand still states that the best way to prevent long Covid is to prevent infection with Covid-19, and that vaccines reduce the risk both by lowering the chance of infection and by reducing the risk that an infection leads to long Covid²⁰. On non-pharmaceutical measures, Health New Zealand has held its position more completely than the United States, the United Kingdom or Canada. Its current public Covid-19 page suggests wearing a face mask, keeping your distance from others when indoors, improving ventilation, coughing or sneezing into your elbow, washing your hands often with warm soapy water, and cleaning surfaces²¹. Its healthy habits guidance recommends masks when visiting healthcare services and encourages them in closed, crowded and confined spaces with poor ventilation²², and masking is further recommended after leaving isolation when visiting healthcare or aged residential care facilities, or when in contact with anyone at risk of becoming seriously unwell²³. New Zealand is one of only three jurisdictions in this survey that still advises the general public to keep their distance indoors.

In New Zealand, the 2026 Immunisation Handbook removed the routine booster recommendation for healthy adults aged 30 to 64, on the grounds that this group is at lower clinical risk of severe infection, though free six-monthly boosters remain available on request, and recommendations remain for older age groups, for Māori and Pasifika people from age 50, and for the immunocompromised²⁴. The epidemiologist Michael Baker publicly urged Health NZ to reconsider, arguing that reduced boosting would lead to more Long Covid, and observing that around nine percent of New Zealanders had experienced some form of the condition²⁴.

Germany’s Federal Institute for Public Health advises that vaccination including recommended boosters is especially important for those at risk of severe illness; that correct hand washing reduces infection risk generally; and that a correctly worn medical mask indoors is additional protection during periods of high viral circulation, such as influenza, Covid-19 or RSV waves, with those at elevated risk particularly encouraged to consider it²⁵. Masks are recommended in indoor spaces where distance cannot be maintained²⁵. The Health Ministry adds that regular burst ventilation is advisable at larger gatherings, and that self-tests can provide additional certainty where many people meet without masks²⁶. The BMG’s Long Covid Initiative states that vaccination offers indirect protection against Long Covid by preventing the infections and reducing illness severity²⁷.

What has changed

First, a lot of the advice has moved from unconditional to conditional. Our 2023 survey could record a straightforward tick for masking or ventilation. Today many agencies recommend the same measures, but hedged advising to do these things when you are symptomatic, during a wave, in crowded indoor settings, or if you are in a high-risk group.

Second, vaccine eligibility has narrowed. The United Kingdom now offers routine NHS vaccination only to those aged 75 and over, care home residents and the immunosuppressed. New Zealand has withdrawn routine booster recommendations from healthy adults aged 30 to 64. The United States has replaced a universal recommendation with individual decision-making. Countries that narrow vaccine recommendations are actually relying on infection to boost immunity.

Third, physical distancing has been dropped by the United Kingdom, Australia and Canada, and is retained as general-public advice only by the WHO, Germany and New Zealand.

What has not changed is the underlying rationale. Every agency that addresses Long Covid directly, the CDC, the WHO, Australian federal and state authorities, Health New Zealand, Germany’s BMG, and Canada’s new CAN-PCC guidelines, still frames avoiding infection as the primary means of prevention.

What the future might hold

Covid-19 researchers have been questioning why there have been low levels of the virus throughout 2026, with some speculating that it might finally have reached stable, low-level endemicity, that it is struggling to evolve to evade immunity, or that it has traded some of its infectious capability for greater persistence. 

UK data may shine some light on the puzzle: through the 2025/26 winter, UKHSA reported Covid-19 circulating at baseline levels while influenza ran at medium levels, with the majority of subtyped influenza viruses being A(H3N2)³⁰. Australia likewise reported unusually high influenza activity in late 2025 with ongoing circulation of influenza A(H3N2) subclade K³¹.

This points to another plausible hypothesis to explain the 2026 lull in Covid-19 transmission that doesn’t involve a change in the virus but instead relies on a change in the population.

Research suggests that prior influenza infection raises interferon levels and reduces the risk of subsequent Covid-19 infection³². In lab-grown human airway tissue, cells infected with influenza A first showed much less SARS-CoV-2 growth afterwards. This seemed to be linked to the cells' innate immune defences, though blocking interferon (one of the main players in that defence) didn't restore the virus's ability to replicate.³³. The same mechanism has been demonstrated in cell culture³⁴ and reviewed across human airway models, animal studies and clinical cohorts, where prior influenza A infection was found to induce a robust type I and III interferon response and broad interferon-stimulated gene upregulation that restricts subsequent SARS-CoV-2 replication within a critical 24 to 72 hour window, while SARS-CoV-2’s own immune evasion means the protection does not run in the opposite direction³⁵. In other words, a recent flu infection may temporarily protect against Covid-19 by activating the body’s antiviral defences. Epidemiologically, Stowe and colleagues found the risk of SARS-CoV-2 infection was 58% lower in influenza A-positive patients³³.

Research also shows that some influenza strains raise interferon levels higher than others, and that H3N2 is particularly notable in this regard. In the airway epithelium work above, a prior A/H3N2 infection reduced the viral RNA load of Omicron by more than three logs, compared with 1.5 logs for a primary A/H1N1 infection³³. Separate work on seasonal influenza lineages has found that H1N1 and H3N2 viruses differ significantly in their ability to antagonise interferon induction and signalling, with the differences segregating primarily with the NS segment³⁶.

It is plausible that the influenza wave of 2025/26 provided a protective effect at a population level, stifling Covid-19’s ability to transmit widely.

With numerous public health agencies around the world now reporting rising levels of Covid-19 in wastewater, the CDC reports Covid-19 growing or likely growing in 43 states, with California among a small number of states at moderate or high wastewater activity, Santa Clara County sewersheds classed as high, and San Francisco recording its highest wastewater levels since last September^37,38, and increases in test positivity, Bay Area positivity reaching 7% for the week ending 1 August, up from 2.7% a month earlier³⁷, and UKHSA reporting hospital PCR positivity in England rising from 0.9% in mid-July to 1.1% and then to 2.2% by 9 August^39,40, it remains to be seen whether we are at the start of a new Covid-19 wave or a blip.

If this is the start of a wave, we know from prior research that antibodies wane over time, so the gap between infections can make a material difference to outcomes and severity. Spike-specific antibody titres fall by roughly half within four months and continue to decline unless re-stimulated by a booster or by reinfection, and individuals who became infected had significantly lower antibody titres at preceding visits than those who did not⁴¹. Neutralising antibody levels wane after an initial peak in vaccinated individuals with a half-life ranging from 29 to 60 days⁴². A Lancet systematic review and meta-analysis assessed how protection against re-infection varies specifically by time since infection⁴³.

We also know that protective antibodies can influence the likelihood of Long Covid. A systematic review covering 58 studies, 53,739 individuals and 7,812 Long Covid patients found that most studies reported an association between anti-spike antibodies and Long Covid, with low anti-spike antibodies during acute Covid-19 associated with increased risk, suggesting that maintaining sufficiently high antibody levels may be protective, though the authors caution that the current evidence level is low⁴⁴. Work published in Nature Immunology found that healthy convalescent individuals had higher titres of neutralising antibodies against SARS-CoV-2 than individuals with Long Covid⁴⁵.

If this hypothesis proves to be well-founded, with what we know about our immune response to SARS-CoV-2 we would expect any negative impact of a longer interval between Covid-19 infections to be most pronounced in children between the ages of 0 to 5, and adults over the age of 75.

We have not yet lived with SARS-CoV-2 long enough to know how it behaves in endemicity, and the question is not only how the virus relates to us but how it settles into the broader ecology of respiratory viruses. 

It seems clear that SARS-CoV-2’s multi-layered immune evasion blunts interferon induction and provides minimal protection against influenza³⁵, and ferrets previously infected with SARS-CoV-2 showed an increased tendency to develop clinical symptoms when subsequently infected with H1N1⁴⁶. Influenza appears to protect against Covid-19 but Covid-19 may do the opposite. If that asymmetry holds at population scale, there is a significant public health implication. A flu wave that suppresses Covid-19 transmission may lengthen the interval between infections, giving more time for antibodies to wane, and a longer gap is not necessarily good news for severity of subsequent infection. Whether that is what happened in 2026, or whether the lull has some other cause entirely is not something we can know for sure at this point. We will need several more years of data before these patterns can be predicted with any confidence, and until then the honest position is that nobody yet knows what Covid-19 looks like in its endemic state.

With all this in mind, it may be useful to remember that although infections may inhibit other infections for a limited period, they are not beneficial to human health. Our primers SARS-CoV-2 Leaves a Lasting Mark on the Immune System and SARS-CoV-2 and "Textbook" Immunity are useful places to begin. As Covid-19 levels rise around the world, it might be prudent to follow the rationale of public health authorities, who almost all say that the key to avoiding Long Covid is to avoid a Covid-19 infection in the first place, and to take precautionary steps to protect oneself. Whatever the narrowing of the past three years, this is still the prevailing advice of leading public health agencies worldwide.