How lengthy does immunity to COVID-19 final?
Antibodies to the virus that causes COVID-19 start to drop within three weeks of infection, research from China suggests.
It had been hoped that people who’d had COVID-19 might develop long-term immunity to further infection. However, studies looking at the levels of IgG antibodies, the type of antibodies that contribute to immunity, suggest this may not be the case.
Researchers studied 1,500 people admitted to hospitals in China with confirmed COVID-19 infection. These patients had antibody tests at least 21 days after admission. Almost 1 in 10 had no detectable IgG antibodies to the SARS-CoV-2 virus when tested. Another study of 37 people with a positive SARS-CoV-2 test but no symptoms, found that 40% had no detectable IgG antibodies two months after the infection.
The findings suggest that many people who recover from COVID-19 may still develop long-term immunity, but a few could remain vulnerable to future infection. Vaccines train the immune system to recognise the virus and are thought, potentially, to confer longer-lasting immunity. So, these data boosts the hunt for a safe and effective vaccine.
Where did the story come from?
The Daily Telegraph is one of a number of news outlets that reported on the two studies. One was published on a pre-print server, meaning it has not been accepted by a medical journal or peer-reviewed. The other is published in the peer-reviewed journal Nature Medicine.
What is the basis for the claim?
The larger, pre-publication study included 1,470 people admitted to hospitals in Wuhan, China, with symptoms of COVID-19, and who tested positive for the virus. After 21 days they had blood tests for IgG antibodies. The vast majority (90%) had IgG antibodies.
The researchers then gave antibody tests to 3,832 healthcare staff from Wuhan who had not been tested for the virus, but where exposure to the virus was assumed. Only 4% demonstrated IgG antibodies, around the same as the general population, where infection levels were expected to be much lower levels. However, it is difficult to form certain conclusions from this as infection among healthcare workers was not confirmed.
The second study from China included 37 asymptomatic people who had tested positive for COVID-19 during contact tracing, and been admitted to hospital for isolation purposes. Around 80% tested positive for IgG antibodies three to four weeks later, the same as a comparison group of 37 people with symptomatic infection. However, a follow-up study around eight weeks later showed 40% of asymptomatic people had lost their IgG antibodies, compared with only 13% of those with symptomatic infection. This could suggest that people with symptomatic infection are more likely to gain longer immunity than those with absent or minimal symptoms. But these are small numbers on which to base firm conclusions.
What do trusted sources say?
In April, BBC News quoted technical lead Dr Maria van Kerkhove from the World Health Organisation who cautioned the value of antibody tests because it is unknown whether people who have contracted SARS-CoV-2 will be immune to further infection.
The CDC also stated that it is not yet known whether people who recover from COVID-19 can get infected again, and emphasise infection control and social distancing measures for all.
- Liu, T et al. Prevalence of IgG antibodies to SARS-CoV-2 in Wuhan – implications for the ability to produce long-lasting protective antibodies against SARS-CoV-2. medRxiv 2020.06.13.20130252; doi: https://doi.org/10.1101/2020.06.13.20130252 (Accessed 30 June 2020).
- Long, Q et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med (2020). https://doi.org/10.1038/s41591-020-0965-6
Analysis by EIU Healthcare, supported by Reckitt Benckiser
- Centres for Disease Control. Coronavirus Disease 2019 (COVID-19). Frequently Asked Questions.