Do I Need A Vaccine If I Already Had Covid-19?

3 min

When you become infected with a virus or receive a vaccine against one, your immune system goes to work — not only fighting the infection or reacting to the vaccine, but also remembering it for the next time you’re exposed to the bug. In some cases that memory can last a lifetime, which is why it’s so rare, although not impossible, for anyone who had measles or chicken pox (or the vaccines for them) to get the illness again. In other cases, the immunity doesn’t last, or a virus mutates enough that it doesn’t trigger the previous memory, and you can get sick again. That’s why we get a new influenza vaccine each year as new strains arise. We have enough data now on COVID-19 to know that infection and inoculation both produce some level of immunity, but that it doesn’t last forever. So yes, even if you’ve already had COVID-19 or had your shots, you should get regular vaccine updates to reduce your risk of becoming sick again.

Since the pandemic began in 2020, we have learned a lot about how our immune response to this virus behaves over time. A 2021 study published in the journal Science looked at blood samples from 188 patients who had recovered from COVID-19 to see how well, and for how long, their immune systems remembered the virus. The investigators looked at four different types of immunological memory (antibodies, memory B cells, and two types of T cells), and found that memory to be robust in 95 percent of patients five to eight months after recovery. Since many people have been infected more than once, we know that immunity is not absolute.

Another study that same year looked at Kentucky residents who had been infected with COVID-19 in 2020 to see how those who had been vaccinated fared against those who had not. It found that of those people who had been infected in 2020, the unvaccinated among them were more than twice as likely to be reinfected in May and June of 2021 than those who had received the shots. That study also noted that immune responses in those previously infected were weak or inconsistent against variants, meaning that immunity based on the original virus may not be enough protection against newer strains.

With a few more years of data available now, we know that infection with COVID-19 protects most people against reinfection for a few months at best. (In those with a compromised immune system, an infection may not provide much protection at all, since the infection may not provoke the immune response required to develop a memory of the virus.) A 2023 analysis showed that immunity had dropped significantly by six months after vaccination, and showed a similar decline nine months after a booster. Vaccine effectiveness against the Omicron variant was weaker than it was against the Delta variant.

The bottom line is that you and your family may not have much, if any, protection against reinfection due to your illness last year. Your best bet is getting vaccinated, and continuing to get regular updates, for more reliable protection.

Andrew Weil, M.D.

Sources
Menegale F, Manica M, Zardini A, Guzzetta G, Marziano V, d’Andrea V, Trentini F, Ajelli M, Poletti P, Merler S. “Evaluation of Waning of SARS-CoV-2 Vaccine-Induced Immunity: A Systematic Review and Meta-analysis.” JAMA Netw Open. 2023 May 1;6(5):e2310650. doi: 10.1001/jamanetworkopen.2023.10650.  PMID: 37133863; PMCID: PMC10157431. pubmed.ncbi.nlm.nih/37133863/

Dan JM, Mateus J, Kato Y, Hastie KM, Yu ED, Faliti CE, Grifoni A, Ramirez SI, Haupt S, Frazier A, Nakao C, Rayaprolu V, Rawlings SA, Peters B, Krammer F, Simon V, Saphire EO, Smith DM, Weiskopf D, Sette A, Crotty S. “Immunological memory to SARS-CoV-2 assessed for up to 8 months after infection.” Science. 2021 Feb 5;371(6529):eabf4063. doi: 10.1126/science.abf4063.  pubmed.ncbi.nlm.nih/33408181/

Cavanaugh AM, Spicer KB, Thoroughman D, Glick C, Winter K. “Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination – Kentucky, May-June 2021.” MMWR Morb Mortal Wkly Rep. 2021 Aug 13;70(32):1081-1083. doi: 10.15585/mmwr.mm7032e1. PMID: 34383732; PMCID: PMC8360277. pubmed.ncbi.nlm.nih/34383732/

Originally Posted September 2021. Updated March 2024