Washington, Oct 14 : People who have taken Johnson and Johnson's Covid vaccine will have better results with a booster shot of either Pfizer or Moderna, finds a study led by the US National Institutes of Health (NIH). The NIH study on "mixing and matching" Covid vaccines included more than 450 adults who were divided into groups and received an extra shot of their original vaccine or a booster from a different company, the CNBC reported. The participants had already taken either of the three vaccines currently available in the country: Pfizer, Moderna or J&J. Antibody levels were measured two weeks and four weeks after the boosters were given. The results, which hasn't yet been peer-reviewed, showed that all the combinations boosted antibody levels higher, but Pfizer's and Moderna's boosters appeared to work best. Booster dose of either the Moderna or Pfizer vaccines increased their antibody responses more often than those who received an extra dose of J&J, the report said. The study showed recipients of Moderna or Pfizer's original vaccines could easily swap third doses; the results were about the same. Volunteers who originally received the J&J vaccine appear to have gotten a better immune response if they got a booster made by Pfizer or Moderna. There were no serious side effects tied to the additional shots and no new symptoms emerged after participants received the booster shots, researchers said. Two participants vomited after their boosters; one had received Moderna and the other J&J. Two other people who got a J&J booster reported fatigue or insomnia. "These data suggest that if a vaccine is approved or authorised as a booster, an immune response will be generated regardless of the primary Covid-19 vaccination regimen," researchers wrote in the study. "Heterologous prime boost strategies may offer immunological advantages to optimise the breadth and longevity of protection achieved with currently available vaccines," they added. J&J's one-dose vaccine uses an adenovirus, while Pfizer's and Moderna's two-dose vaccines use mRNA technology. Scientists believe that by "mixing and matching" vaccines that use different platforms, people may be able to get broader protection against the coronavirus and its new variants. /IANS